How can I make a public static class "secure"?

I'm looking to create a secure wrapper for a public class with public static methods, so let's say the class is very simply:

public class MyClass {
      public static int Add (int first, int second)
      {
          return first + second;
      }
}

I want to have a client needing to access this via some secure other class that will call MyClass. At the end of the day I'm expecting to have all this code in a single dll for clients to use. The intention is to have some behaviour like:

public class SecureMyClassWrapper
{
    bool _isUnlocked;
    private static readonly List<string> validIds = new List<string>(){"only me", "and them"};

    public SecureMyClassWrapper(string id)
    {
        if (validIds.Contains(id))
        {
            _isUnlocked = true;
        }
        else
        {
            _isUnlocked = false;
        }
    }

    public int Add(int first, int second)
    {
        if (_isUnlocked)
        {
            return MyClass.Add(first, second);
        }
        else
        {
            // throw security exception etc.
        }
    }
}

There's a fair possibility that someone with more hacking ability than me is going to want to get at my static methods, so please can somebody suggest why this might be a bad approach or what I should be concerned about here? Some ideas would be that

• MyClass methods can easily be called through reflection


• somebody could ildasm.exe code, change the list of validIds or _isUnlocked logic (or even their values at runtime?)


• possible to read a valid ID and then use it as their own

How could I guard against reflection or decompilation in these cases? Is there a standard approach for this you would recommend, e.g. Code Access Security?